Fuse link



E. F. BOOTHE Sept. 2l, 1937.

FUSE LINK Filed sept. s, 19:55

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Patented Sept. 21, 1937 PATENT OFFICE FUSE LINK Eugene F. Boothe, St.

Louis, Mo., assignor to James R. Kearney Corporation, St. Louis, Mo., acorporation of Missouri Application September 4 Claims.

This invention relates generally to fuse links, and more specifically tofuse links of the tension type, the predominant object of the inventionbeing to provide a tension type fuse link which is 5 of such improvedconstruction and arrangement that it is possessed of much greatertensile strength than were the tension fuse links heretofore known.

Fuse links of the type referred to above ordi.- narily are adapted to beheld under mechanical tension produced either by spring means which formparts of the fuse link structures or parts of the protective apparatuswith which the fuse links are associated, the purpose being to create awide gap between the severed ends of the fusible element of the fuselink after the same has become ruptured by passage of abnormal current,and to quickly extinguish any arc attending the blowing of the fusibleelement by causing the ruptured ends thereof to fly apart under theaction of the spring tension.

A heretofore prevailing diiiiculty inherent in tension fuse links,particularly those of low or fractional ampere current carryingcapacity, results from the tendency of the fusible element to becomesevered by reason of the mechanical forces applied thereto, or if' notactually severed the application of such forces to the fusible elementfor a long period of time results in alteration of the operatingcharacteristics, or rating of the fuse link. In other words, it has beendetermined that an unstressed fuse wire which is intended to becomeruptured upon passage therethrough of, say, three-fourths of an ampere,when held under mechanical tension of the order produced by spring meansfound in the usual types of protective apparatus, is ruptured bycurrents of a magnitude substantially less than the figure specified.

The purpose of this invention, therefore, is to provide a fuse linkconstruction which will not be harmfully affected by the-applicationthereto of relatively high mechanical forces by relieving in an improvedmanner the fusible element of the improved fuse link structure of theforces produced by the tensioning means.

Fig. 1 is a, view partly in vertical section and partly in sideelevation of a fuse cartridge havingthe improved fuse link associatedtherewith. Fig. 2 is a fragmentary view of a portion ofthe structureillustrated in Fig. 1, but viewing same from a different angle. Y

In the drawing, wherein is shown for the purpose of il1ustration,merely,one embodiment of the invention, A designates a fuse cartridge adjacentto the lower end of which a terminal member 3, 1935, Serial No. 38,876

B is fixed, said terminal member B being adapted to aid in electricallyassociating the fuse cartridge A with a switch apparatus (not shown). Atits upper end the fuse cartridge A has associated with it an adapter Cwhich comprises a short tubular portion CEL that is extended downwardlyinto the upper portion of the fuse cartridge, and an outstanding annularflange Cb which contacts with the top face of said fuse cartridge.

The improved fuse link includes a contact head l which is xedly locatedat the outer end of a strip 2 of conducting material, said contact headbeing arranged in contact with the top face of the flange Cb of theadapter C, and said strip 2 being extended downwardly into the cartridgeA. EX- tended upwardly through the fuse cartridge A is an electricalconductor 3 which serves as a terminal element of the fuse link, the end3 of said conductor which is located within the fuse cartridge beingspaced a considerable distance from the inner or lower end of the strip2. The opposite end portion of the conductor 3 is turned about the lowerend of the fuse cartridge and is extended upwardly with respect thereto,as indicated at 3a in Fig. 1, said upwardly extended portion of saidconductor being mechanically and electrically clamped to the terminalmember B through the instrumentality of a clamping screw D.

The strip 2 and the conductor 3 are connected together by connectingmeans 4, which comprises a pair of strain wires 5 and 3, and a bead orring l formed of electrical insulating material. The strain Wire 5 ispassed through an aperture 8 formed through the strip 2 and is loopedthrough the bead or ring 1, as shown most clearly in Fig. 1, andportions of said strain wire are twisted together as indicated at 5 todraw the side portions thereof together. The strain wire 6 is alsolooped through the bead or ring 1, and said strain wire 6 is secured tothe conductor 3 by having a portion thereof wrapped or twisted aboutsaid conductor, by preference-parallel portions 6 of said strain Wire 6being extended longitudinally of the conductor 3 in contact therewith,and the end portions la of the strain wire being Wrapped about the endportion of the conductor 3 in a manner to embrace both the conductor 3and the portions 6 of the strain wire. If desired, solder may beemployed to securely fix the strain Wires to the strip 2 and theconductor 3.

The fusible element 9 of the fuse link is secured by solder or othersuitable means at its opposite ends to the strip 2 and to the conductor3. 'Ihe fusible conductor is bowed outwardly slightly, as

shown to the best advantage in Fig. 1, so as to be out of electricalcontact with the strain wires 5 and 6.

Extended downwardly from the strip 2 is an expulsion tube I formed ofelectrical insulating material which embraces the extreme lower portionof the strip 2, the connecting means 4, and a portion of the conductor3, the lower portion 2' of the strip 2 which extends into the expulsiontube being of reduced width and said strip being provided with shoulders2a with which the upper edge of the expulsion tube contacts (see Fig.2). Extended upwardly into the expulsion tube from a point aconsiderable distance below the lower edge of said expulsion tube is anelongated tubular element II which at its lower end is provided with anoutstanding, annular flange I2, and an expansible coil spring I3 isinterposed under compression between said annular flange I2 of thetubular element II and the lower edge of the expulsion tube Ill. Abutton I4 is secured to the conductor 3, and this button holds thetubular element in itselevated position so that the coil spring ismaintained in compression.

In the use of the improved fuse link, the strain wires 5 and 6 are notin electrical contact with each other because of the presence of theinsulating bead or ring 'I which separates the inner end portion of saidstrain wires from each other, hence all electrical current conducted bythe fuse link must low through the fusible element 9. When a faultoccurs in the line protected' by the improved fuse link, the fusibleelement 9 melts and the current flows through the strain wires passingfrom one to the other in the form of an arc. The arc thus producedbreaks one or both of the strain wires, allowing the ends to be pulledapart by the associated switch mechanism or by the coil spring I3. Theimportance of the insulating bead or ring resides in the fact that asmall fraction of an ampere through an arc will break a strain wire ofthe required strength, whereas, if the strain wire were continuousseveral amperes would be required in order to melt r the strain wire andbreak the circuit.

It is obvious, therefore, that the connecting means 4 of the improvedstructure entirely relieves the fusible element 9 of all tensionalstrains exerted by the coil spring I3 or by parts of a 0 switch withwhich the fuse link is associated, and

therefore the danger that the fusible element might be ruptured orotherwise injured by mechanical strains applied thereto is eliminated- Iclaim:

1. A fuse link assembly including a, pair of spaced terminal members, afusible element for electrically connecting 4said terminal members,connecting means for mechanically connecting said terminal members so asto relieve said fusible element of tension applied to the fuse linkassembly, said connecting means comprising strain elements mechanicallyand electrically connectconnecting means for mechanically connectingsaidterminal members so as to relieve said fusible element of tensionapplied to the fuse link assembly, said connecting means comprisingstrain elements mechanically and electrically connected respectively tosaid terminall members at their outer remote ends and formed ofelectrical conducting material, and means formed of electricalinsulating material for connecting the inner adjacent ends of saidstrain elements together in spaced relation so that they are out ofdirect electrical connection with each other.

3. AY fuse link assembly including a pair of spaced terminal members, afusible element for electrically connecting said terminal members,connecting means for mechanically connecting said terminal members so asto relieve said fusible element of tension applied to the fuse linkassembly, said connecting means comprising strain elements mechanicallyand electrically connected respectively to said terminal members attheir outer remote ends and formed of electrical conducting material,and means comprising an annular member formed of insulating material forconnecting the inner adjacent ends of said strain elements together inspaced relation so that they are out of direct electrical connectionwith each other.

4. A fuse link assembly including a pair of spaced terminal members, afusible element for electrically vconnecting said terminal members,connecting means for mechanically connecting said terminal members so asto relieve said fusible element of tension applied to the fuse linkassembly, said connecting means comprising strain wires mechanically andelectrically connected respectively to said terminal members at theirouter remote ends and formed of electrical conducting material, and amember formed of insulating material through which said strain wires arelooped for connecting the inner adjacent ends of said strain wirestogether in spaced relation so that they are out ofA direct electricalconnection with each other.

` EUGENE F. BOOTHE.

